If 6xy = x2y + 9y, what is the value of xy? (1) x = 2 (2) x

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If 6xy = x2y + 9y, what is the value of xy? (1) x = 2 (2) x [#permalink]

05 Jan 2009, 19:26

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If 6xy = x2y + 9y, what is the value of xy?

(1) x = –2

(2) x = 3

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Re: DS: Equations 2 [#permalink]

05 Jan 2009, 22:47

pmenon wrote:

If 6xy = x2y + 9y, what is the value of xy?

(1) x = –2

(2) x = 3

In the above quesion I am assuming x2y = x^2*y

(1)
x=-2
-12y = 9y+9y --->30y=0
->y=0
xy=0
suffcient
(2)
x=3

18y=9y+9y --> 18y=18y
---> we don't get single solution from this equation
Y can be any thing
not sufficient

A is the answer.
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Re: DS: Equations 2 [#permalink]

06 Jan 2009, 13:17

x2suresh wrote:

pmenon wrote:

If 6xy = x2y + 9y, what is the value of xy?

(1) x = –2

(2) x = 3

how did you get 9y for X^2y. shouldn't it be 4y

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Re: DS: Equations 2 [#permalink]

06 Jan 2009, 14:39

is there a typo in the original equation?
6xy = x2y+9y
If we treat x2y = 2xy;
4xy=9y=>y=0 or x=9/4.
So problem is solved from question stem itself.
Now if x2y = X^2*y; here is the soltuion:
6xy = x^2*y+9y=(x^2+9)*y
y=0 or
x^2-6x+9=0;
(x-3)^2 = 0 and hence x=3.
If x=3, we still need another equation to solve for y. So, (2) is not enough.
If x=-2,
-12y = 4y+9y=>-12=13 if y=!0. Thus, y=0 and xy can be determined. Hence, (1) is enough.

Answer A.

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Re: DS: Equations 2 [#permalink]

06 Jan 2009, 15:08

ALD wrote:

x2suresh wrote:

pmenon wrote:

If 6xy = x2y + 9y, what is the value of xy?

(1) x = –2

(2) x = 3

how did you get 9y for X^2y. shouldn't it be 4y

you are right.. it should be 4y .. type mistake..

anyway it should lead to the answer A
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Re: DS: Equations 2 [#permalink]

06 Jan 2009, 16:11

my bad guys, x2y = x^2y.

And yes, A is the correct answer

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Re: DS: Equations 2 [#permalink]

07 Jan 2009, 07:17

The equation: 6xy=x2y+9y
equivalent to y(x-3)^2=0
means: x=3 or y=0
A, x=-2 => y=0
B/ x=3=> insulf to determine y

hence A is the best answer

Re: DS: Equations 2 [#permalink] 07 Jan 2009, 07:17

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If 6xy = x2y + 9y, what is the value of xy? (1) x = 2 (2) x

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If 6xy = x2y + 9y, what is the value of xy? (1) x = 2 (2) x

If 6xy = x2y + 9y, what is the value of xy? (1) x = 2 (2) x

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